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Investigators from the Perris Police Department and the Riverside County Sheriff's Department met with the girl, they said she looked emaciated and only 10 years old, even though she was 17.

After interviewing the girl, investigators contacted her parents, David Allen Turpin, 57, and Louise Anna Turpin, 49, at the home from where the teenager escaped.

"Further investigation revealed several children shackled to their beds with chains and padlocks in dark and foul-smelling surroundings, but the parents were unable to immediately provide a logical reason why their children were restrained in that manner," a police statement read.

"The victims appeared to be malnourished and very dirty," the statement continued.

"All 13 victims, ranging from the age of two to 29, were transported to the Perris Station and interviewed.

"Both parents were detained and transported to the station for further investigation.

'Things 1 to 13': The family are seen in Dr Seuss-style shirts, and all in blue jeans, in a family photo taken in April 2016. Photo / Supplied

State Department of Education records show the family home has the same address as Sandcastle Day School, where David Turpin is listed as principal. In the 2016-17 school year it had an enrollment of six with one student in each of the fifth, sixth, eighth, ninth, 10th and 12th grades.

Neighbours said they were stunned by the arrests. Andrew Santillan, who lives around the corner, heard about the case from a friend.

"I had no idea this was going on," he told the Press-Enterprise of Riverside. "I didn't know there were kids in the house."

Other neighbours described the family as intensely private.

A few years ago, Robert Perkins said he and his mother saw a few family members constructing a Nativity scene in the Turpins' front yard. Perkins said he complimented them on it.

"They didn't say a word," he said.

The Turpins filed for bankruptcy in 2011, stating in court documents they owed between US$100,000 and US$500,000, The New York Times reported. At that time, Turpin worked as an engineer at Northrop Grumman and earned US$140,000 annually and his wife was a homemaker, records showed.

Their bankruptcy lawyer, Ivan Trahan, told the Times he never met the children but the couple "spoke about them highly."

"We remember them as a very nice couple," Trahan said, adding that Louise Turpin told him the family loved Disneyland and visited often.